In GLSL ES 3.00, float literals are allowed to have an 'f' or 'F'
suffix, but they don't change the parsing process since they're always
interpreted as single-precision IEEE-754 floating-point values.

The std::istringstream used for parsing the literal's string can have
implementation dependent behavior depending on the presence of the
suffix, so this change removes it. This matches what ANGLE does.

Fixes: b/168250854
Change-Id: I203833a2e817ca698894db5669941fb435b97868
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48388
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>