[core] Remove re-linking programs approach (#14482)

Remove re-linking programs as redundant.
It costs (cheaper to link once than twice) and (subjective) is not that common GL API
usage pattern, although perfectly legal and permitted.
Initial idea, behind the removed code, was to enable work on optimization
that would reduce number of attrib setup calls in case when VAO is not
available (as described in #9433).

As such optimization is not implemented, and it is arguable if it makes sense
to do it now, we can remove re-linking.

Related to closed PRs #9433 and PR #11583.

I have [measured the time spent just on relinking](https://gist.github.com/astojilj/29bd5a5c5dc0b2d9f29ecb660da07fbf) using release build on iPhone SE (A9, same as iPhone 6S):

- 1st run after reboot or installation
Total 37.14ms, average per program:1.86ms

- reopening
Total: 2.47ms, average per program: 0.12ms

This time we save using the patch here.

1 files changed, 5 insertions, 33 deletions

diff --git a/src/mbgl/gl/attribute.cpp b/src/mbgl/gl/attribute.cpp
index 4983a8c204..d5240b5b7a 100644
--- a/src/mbgl/gl/attribute.cpp
+++ b/src/mbgl/gl/attribute.cpp
@@ -1,47 +1,19 @@
 #include <mbgl/gl/attribute.hpp>
 #include <mbgl/gl/context.hpp>
-#include <mbgl/gl/defines.hpp>
 
 namespace mbgl {
 namespace gl {
 
 using namespace platform;
 
-void bindAttributeLocation(Context& context, ProgramID id, AttributeLocation location, const char* name) {
-    // We're using sequentially numberered attribute locations starting with 0. Therefore we can use
-    // the location as a proxy for the number of attributes.
-    if (location >= context.maximumVertexBindingCount) {
-        // Don't bind the location on this hardware since it exceeds the limit (otherwise we'd get
-        // an OpenGL error). This means we'll see rendering errors, and possibly slow rendering due
-        // to unbound attributes.
+optional<AttributeLocation> queryLocation(ProgramID id, const char* name) {
+    GLint attributeLocation = MBGL_CHECK_ERROR(glGetAttribLocation(id, name));
+    if (attributeLocation != -1) {
+        return attributeLocation;
     } else {
-        MBGL_CHECK_ERROR(glBindAttribLocation(id, location, name));
+        return {};
     }
 }
 
-std::set<std::string> getActiveAttributes(ProgramID id) {
-    std::set<std::string> activeAttributes;
-
-    GLint attributeCount;
-    MBGL_CHECK_ERROR(glGetProgramiv(id, GL_ACTIVE_ATTRIBUTES, &attributeCount));
-
-    GLint maxAttributeLength;
-    MBGL_CHECK_ERROR(glGetProgramiv(id, GL_ACTIVE_ATTRIBUTE_MAX_LENGTH, &maxAttributeLength));
-
-    std::string attributeName;
-    attributeName.resize(maxAttributeLength);
-
-    GLsizei actualLength;
-    GLint size;
-    GLenum type;
-
-    for (int32_t i = 0; i < attributeCount; i++) {
-        MBGL_CHECK_ERROR(glGetActiveAttrib(id, i, maxAttributeLength, &actualLength, &size, &type, &attributeName[0]));
-        activeAttributes.emplace(std::string(attributeName, 0, actualLength));
-    }
-
-    return activeAttributes;
-}
-
 } // namespace gl
 } // namespace mbgl